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Hot Jupiters
Hot Jupiters AKA roaster planets, epistellar jovians, pegasids or pegasean planets are a class of planets whose characteristics are similar to Jupiter, but that have high surface temperatures because they orbit very close—between 0.015 and 0.5 astronomical units (2.2×106 and 74.8×106 km)—to their parent stars, whereas Jupiter orbits its parent star at 5.2 astronomical units (780×106 km), causing low surface temperatures. One of the best-known hot Jupiters is Bellerophon, (51 Pegasi b). Discovered by Earthers in 1995, it was the first planet they found orbiting a Sol-like star. 51 Pegasi b has an orbital period of about 4 days. Common Characteristics Hot Jupiters have some common characteristics: *They have similar characteristics to Jupiter, however, they orbit much more closely to the star and experience a high surface temperature. *They have a much greater chance of transiting their star as seen from a farther outlying point than planets of the same mass in larger orbits. Due to high levels of solar irradiation they are of a lower density than they would otherwise be. *They are all thought to have migrated to their present positions because there would not have been enough material so close to the star for a planet of that mass to have formed in situ. *Most of these have nearly circular orbits because their orbits have been circularized, or are being circularized, by the process of libration. *They exhibit high-speed winds distributing the heat from the day side to the night side, thus the temperature difference between the two sides is relatively low. *They are more common around F- and G-type stars and somewhat less common around K-type stars. Hot Jupiters around red dwarfs are very rare. *Hot Jupiters induce oscillations in their parent stars' motion that are relatively large and rapid, compared to other known types of planets. Formation Theory They are thought to form at a distance from the star where the planet can form from rock, ice and gases. The planets then migrate inwards to the star where they eventually form a stable orbit. The planets usually move by type 2 migrations, or possibly via interaction with other planets. The migration happens during the solar nebula phase, and will typically stop when the star enters its T-Tauri phase. The strong stellar winds at this time remove most of the remaining nebula. After their atmospheres and outer layers are stripped away, their cores may become chthonian planets. The amount of the outermost layers that is lost depends on the size and the material of the planet and the distance from the star. In a typical system a gas giant orbiting 0.02 AU around its parent star loses 5–7% of its mass during its lifetime, but orbiting closer than 0.015 AU can mean evaporation of the whole planet except for its core. Terrestrial planets in systems with hot Jupiters Planets up to two Earth masses are able to form in the habitable zone after the hot Jupiter passed through and its orbit stabilized. Due to the mixing of inner-planetary-system material with outer-planetary-system material from beyond the frost line, the terrestrial planets that formed after a hot Jupiter's passage are usually particularly water-rich. Category:Planets